Factors associated with reactogenicity to an investigational HIV vaccine regimen in HIV vaccine trials network 702

Highlights • Those assigned female at birth experience more reactogenicity.• Most symptoms are mild.• Pain and/or tenderness symptom common in both vaccine and placebo groups.


Introduction
Reactogenicity encompasses the short-term subjective and objective physical manifestations of the inflammatory response to vaccination.Local reactogenicity symptoms include reported pain, and objective measurements of redness, and swelling at the injection site.Systemic reactogenicity symptoms include fever, and subjective reports of fatigue, headache, myalgia, arthralgia, chills and nausea [1].
Reactogenicity contributes to negative attitudes and reduced uptake of vaccines [2].In one systematic review, safety and side effects concerns (including the life-threatening and severe, like thrombotic thrombocytopenia syndrome, myocarditis and pericarditis) affected COVID-19 vaccine acceptance [3].Multiple factors influence reactogenicity.A study of health-sector employees found that female sex and Hispanic ethnicity were associated with higher odds of reporting systemic reactogenicity symptoms after a COVID-19 vaccine than male sex and other ethnicities [4].Limited reactogenicity data exist for African adults due to few vaccination programs.
As the search for an efficacious HIV vaccine continues, elucidating factors associated with reactogenicity may help researchers optimize safety and tolerability.HVTN 702, demonstrated that although the vaccine regimen induced antibody and/or cellular immune responses in about two-thirds of vaccine-recipients, there was no protective efficacy [5].Very few HVTN 702 participants discontinued study product due to related adverse events [6]; therefore analysis of participant characteristics associated with these events was not conducted.Nonetheless, reactogenicity was reported by about one-third of placebo-recipients and 46 % of vaccine-recipients [6].We investigated clinical, sociodemographic and laboratory variables associated with reactogenicity in HVTN 702.

Study participants
Between 2016 and 2019, HVTN 702 enrolled 5404 adults without HIV infection, aged 18-35 years from 14 sites in South Africa.This ancillary analysis included all participants who received at least one injection of vaccine or placebo.We analyzed by treatment received, not by randomization allocation, to account for rare errors in product administration.

Outcome variables
Post-vaccination, participants were observed for 30 min in clinic, trained to use a paper tool to log symptoms and instructed to present to clinic if concerning symptoms arose.After 3 days, researchers contacted participants to record reactogenicity data, and followed symptoms until resolution.Participants who self-reported a grade of greater than "mild" were seen by a clinician within 48 h.
The number and percentage of participants who experienced each reactogenicity sign or symptom were summarized by treatment received and grade (none/non gradable, mild/grade 1, moderate/grade 2, severe/grade 3 and life-threatening/grade 4).Each participant's reactogenicity sign or symptom was counted once under the maximum severity for all injection visits.These clinical, sociodemographic and laboratory test result characteristics were summarized by treatment received: age at randomization, age category at randomization (18-21, 22-25, 26-35 years), sex assigned at birth, gender identity (female, male, other), sexual orientation, race, body mass index (BMI), BMI category, number of live births (for participants with childbearing potential), geographic region, education level, married/have main partner status, urban living area, formal dwelling, and sexually transmitted infection (STI) status at baseline (available for participants enrolled after protocol version 2.0).Univariate and multivariate logistic regression were performed to assess associations between reactogenicity and sociodemographic and laboratory variables.Kruskal-Wallis tests were used to test for differences in reactogenicity severity between groups.

Ethical considerations
Research ethics committees of the Universities of the Witwatersrand, Cape Town, KwaZulu-Natal, Sefako Makgatho, and South African Medical Research Council approved the HVTN 702 trial.All study participants signed an informed consent document that provided study purpose, duration, procedures, alternatives, risks and benefits.

Baseline characteristics
In HVTN 702, 2706 participants received the investigational vaccine, and 2698 received placebo.Vaccine and placebo groups had similarly distributed baseline characteristics (Appendix 1).
In the multivariate analysis (Appendix 1), frequency of reactogenicity was 2.5 times higher in those assigned female than those assigned male at birth in vaccine-recipients (OR = 2.50, p < 0.001) and almost 2 times higher in placebo-recipients (OR 1.81, p < 0.001), after accounting for other variables (age, BMI, region, education, main sex partner, type of living area, baseline STI status, complete blood count [CBC] status).For vaccine-recipients only, after accounting for the same variables, every additional year of age was associated with a 3.0 % increase in frequency of reporting reactogenicity (OR = 1.03, p = 0.002).Region was associated with different reactogenicity in vaccine and placebo groups, after adjusting for the same variables, with 1.4 times more frequent reactogenicity reported by vaccine-recipients from Cape than vaccine-recipients from central provinces (OR 1.40, p = 0.008) and 1.3 times higher among placebo-recipients from Cape than central provinces (OR = 1.33, p = 0.028).Those in KwaZulu-Natal reported reactogenicity significantly less frequently than those in central provinces in both (vaccine OR = 0.46, p < 0.001, placebo OR = 0.42, p < 0.001) groups.

Discussion
In this ancillary analysis, those assigned female sex at birth, vaccinerecipients with increasing age and those living in the Cape provinces reported any reactogenicity more frequently.Overall, the vaccine was well-tolerated with mostly mild symptoms; the commonest were local pain and/or tenderness and headache.Both subjective and objective symptoms were more frequent in vaccine-recipients.
Findings are consistent to the RV144 trial with similar products, ALVAC-HIV and AIDSVAX B/E, in which pain and tenderness was the commonest local reactogenicity and symptoms were mostly mild to moderate [7] while mostly mild for HVTN 702.For both trials, moderate to severe local and systemic reactogenicity were more common in vaccine-recipients than placebo-recipients.
More participants assigned female, regardless of treatment assignment, reported reactogenicity than participants assigned male at birth.This is expected because compared to those assigned male, vaccinerecipients assigned female sex at birth experience more vaccine adverse events [1,[8][9][10][11].Females often develop higher vaccine-induced antibody titres than men, influenced by genetic and hormonal differences [9].Sex hormones affect immune responses and cytokine levels, with oestrogens being immunostimulant and androgens being relatively immunosuppressive [10,12,13].Females also develop greater immune responses to infection [14,15].
Adults older than 60 years have reduced reactogenicity and immune responses to immunization than younger people [16].However, in this group of participants aged 18-35 years, we saw small but statistically significant increases in reactogenicity with increasing age.Our study suggests that age-related reactogenicity patterns may differ by vaccine.However, more research is needed into whether increasing age correlates with increased reactogenicity for other types of HIV vaccines.
We found similar regional differences in reactogenicity in both groups, with more reactogenicity in the Western/Eastern Cape provinces than other regions.Geographic location may indirectly affect reactogenicity by influencing immune responses through socio-economic dynamics, genetics, climate, sun exposure, nutrition, and/or comorbidities [17].There may have been differences in administration of the vaccine, although unlikely given standardized study staff training and monitoring.There may be social, behavioral and cultural differences in illness experiences post-vaccination [1].
Future HIV vaccine trials are likely to continue to examine sequential, multi-dose regimens with differing formulations over time.The experience in this trial suggests that local and systemic reactogenicity symptoms to similar regimens are to be expected in approximately 20 % of the adult population.Placebo-recipients report a substantial number of reactogenicity symptoms; trial participants should be counseled that they cannot predict their treatment assignment from reactogenicity [7,11].
We analyzed one vaccine regimen and thus cannot yet generalize our findings about the associations between age, and sex at birth, and reactogenicity.However, our findings are supported by research on non-HIV vaccines: somethough not allstudies observed that women reported more reactogenicity than men from human papillomavirus (HPV) and H1N1 influenza vaccines [1] Reports about regional variation in HIV vaccine reactogenicity are scarce, and it is still unclear if, as we suspect, region is a proxy indicator for other phenomena.Ongoing research is assessing whether the same patterns of reactogenicity can be extrapolated to other HIV vaccine regimens.
We did not analyze findings by subjective versus objective reactogenicity, nor by the presence of adjuvants in the vector vaccine or not, nor by total number of injections over time, given the six-injection regimen.
Placebo and multi-dose, extended vaccine injections in the HVTN 702 trial for HIV prevention were well tolerated and most local and systemic reactogenicity was mild.Common symptoms like headache were reported similarly regardless of the treatment received.All participants in vaccine trials of similar agents should continue to be informed about possible reactogenicity.

Author confirmation
All authors attest they meet the ICMJE criteria for authorship.

Funding
Funding was provided to Novartis Vaccines and Diagnostics (now part of the GlaxoSmithKline SA) by NIAID (HHSN272201300033C// HHSN272201600012C) for the selection and process development of the two gp120 envelope proteins TV1.C and 1086.C, and by the Bill & Melinda Gates Foundation Global Health Grant OPP1017604 and NIAID for the manufacture and release of the gp120 clinical grade material.GlaxoSmithKline Biologicals SA has contributed financially to provision of pre-exposure prophylaxis for participants.GlaxoSmithKline Biologicals SA was provided the opportunity to review a preliminary version of this manuscript for factual accuracy, but authors are solely responsible for final content and interpretation.

Table 1
Baseline characteristics of study participants in HVTN 702 according to treatment received.

of babies alive at birth among participants assigned female at birth
Question introduced after study began and asked retrospectively when required.It is missing for participants who were lost to follow up prior to its introduction.** Sexually transmitted infections (Syphilis, Chlamydia/Gonorrhea, Trichomonas Vaginalis) at baseline only available on participants enrolled under protocol version 2.0 and higher. *

Table 2
Comparison of local and systemic reactogenicity symptoms by treatment received in the HVTN 702 trial.